1. Field of the Invention
This invention relates to an electronic level and specifically to the visual display and calibration of the level.
2. Description of the Related Art
Electronic levels known in the art include that sold by Wedge Innovations Inc. and as disclosed in U.S. Pat. No. 4,912,662 issued Mar. 27, 1990 to Butler et al. (assigned to Wedge Innovations Inc.). Such prior art electronic levels display show the inclination in degrees or percent slope, which are typically not the inclination measurements used by building tradesmen or others.
Prior art devices thus often do not provide a satisfactory indication of deviation from level or plumb in a useful manner.
An electronic level disclosed in International (PCT) Patent Application No. PCT/US93/07434 published Mar. 3, 1994 having International Publication Number WO94/04888 and entitled "Electronic Level . . .", invented by Charles E. Heger et al. (docket no. M-2167-1P PCT), includes a graphical display of rise over run (deviation from a null) in inches per the actual length of the level instrument (such as two or four feet). The display includes a number of parallel line segments resembling a typical ruler scale as the primary indication. When the device is at a null (level or plumb or at some other preselected inclination), only the central line segment is illuminated. When the device is inclined at an angle from the null, one or more of the line segments are illuminated starting from the center line segment. The more line segments that are illuminated starting from the center line segment, the greater the amount of inclination indicated. Each line segment in one embodiment indicates 1/64th inch of additional inclination per horizontal foot. The line segments on either side of the central line segment thus provide an indication of inclination in either direction, i.e. that the left end or right end of the device is inclined. Additionally, numerals associated with the scale show the amount of inclination per arbitrary length (such as two feet or four feet) related to the instrument length. Also included is a slope indicator and a numerical indicator for indicating a fixed offset mode.
Also included is a direction of rotation indicator for showing by means of arrows and associated line segments in which direction one must rotate the device to achieve the null position.
However, these earlier devices do not fully solve the problem of an easily read and intuitively understood display providing a graphic depiction of the amount and direction of derivation from null.